# Subnet / CIDR calculator — no upload

> Calculate subnet ranges, netmask, network and broadcast addresses, and host counts from CIDR notation, in your browser. Nothing is uploaded.

Enter a CIDR block like 10.0.0.0/24 to get the netmask, network and broadcast addresses, usable host range, and host count. It calculates in the browser with no upload.

Subnetting means constant CIDR arithmetic — how many hosts fit, where a range starts and ends, what mask a prefix implies. A calculator removes the error-prone binary math when planning networks and firewall rules.

For address conversion use the IP converter; for the ports you'll open, the common ports reference.

## How to

1. **Enter CIDR.** Type an address with a prefix, e.g. 192.168.1.0/24.
2. **Calculate.** See the range, mask, and host count.
3. **Use it.** Plan your subnetting or firewall rules.

## FAQ

### How many hosts are in a /24?

256 addresses, 254 usable (excluding network and broadcast). The calculator shows the counts for any prefix so you don't compute powers of two by hand.

### Does it support IPv6?

It handles CIDR math; for IPv6 address form specifically, pair it with the IP converter for expansion and compression.

### Is anything uploaded?

No. Subnet math is done locally in the tab.


## Related tools

- [IPv4 / IPv6](https://www.safepaper.app/dev/ip-convert)
- [Common ports](https://www.safepaper.app/dev/common-ports)
- [MAC / OUI](https://www.safepaper.app/dev/mac-lookup)
- [User-Agent parser](https://www.safepaper.app/dev/user-agent)

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Canonical HTML: https://www.safepaper.app/dev/cidr
Markdown: https://www.safepaper.app/dev/cidr.md

There is no upload endpoint — your files are processed in this browser tab. Open your network tab and check.